The present invention relates to the field of printed circuit boards. More specifically, the invention relates to the field of conducting heat from circuit board mounted components.
Electronic components generate heat when in operation. Some of this heat is normally dissipated to the surroundings. The amount of heat dissipated to the surroundings will depend on the temperature difference between components and their surroundings, the material from which the components are made, and by the ability of the surroundings to absorb heat. The larger the temperature difference, the quicker heat is dissipated; and the more the material from which the component is made dissipates heat, the more heat that will be dissipated. Compare, for instance, a thermos flask with a metal coffee pot. The heat absorbing capacity of the surroundings also plays a part, which is why water can be felt to be colder (or hotter) than air at the same temperature.
Heat that is not emitted to the surroundings will heat the individual components. Although this may sometimes be desirable, it creates a problem in many cases since the component can become too hot and therewith damage itself. In these cases the component will preferably be protected by ensuring that it dissipates more heat, by increasing its heat dissipating properties, by lowering the ambient temperature, or by increasing the heat absorption capacity of the surroundings.
The heat dissipating properties of a component may, of course, often be determined when producing the component oneself or when placing a special order for the component concerned. However, the component used is normally a ready-made component, meaning that it is difficult or impossible to influence the design of the component.
The amount of heat emitted by a component will increase when the temperature of the surroundings is lowered. This can be achieved in several ways, for instance with the aid of cooling fins, fans, heat exchangers, self-convection with air, immersing the component in liquid nitrogen, and so on. The use of liquid nitrogen is a very complicated and expensive procedure, and hence simpler devices are preferred, such as cooling fins and fans, albeit the use of fans or blowers may be impossible in many instances. Although cooling fins and fans (blowers) function effectively with respect to individual components, it may be difficult for such cooling devices to fulfill their function when the component is surrounded by several other components, for instance on a printed circuit board. The closer together the components are, the more difficult it is to cool said components since they heat-up the surroundings of each other.
The trend within the electronic industry is towards smaller equipment, and consequently printed circuit boards have also become smaller. The components on a small printed circuit board are closer together than on a large board. One way of partially avoiding components from heating each other""s surroundings is to place high heat-dissipating components far away from each other. This solution, however, can result in a highly complicated circuit board pattern, i.e. the pattern of conductors that electrically interconnect the components.
However, miniaturisation will result sooner or later in components being placed so close together that they indirectly heat-up each other, despite efforts to keep the temperature down. This problem can be solved by applying the third method, in which the heat absorbing capacity of the surroundings is increased. This can be achieved by placing the component in contact with a metal heat sink. Since many metals are effective heat sinks, call to mind a frying pan in this respect, the heat sink is able to carry away heat more effectively than air. The distal end of the heat sink may, in turn, be connected to a cooling fin. The large surface area of the cooling fin is able to cool the component effectively and indirectly. This allows components that have a large heat loss to be placed close to other components on a printed circuit board without heating these other components or the surroundings excessively.
U.S. Pat. No. 5,779,134A teaches a method of mounting heat sink elements on a printed circuit board. In brief, the method involves the steps of covering a number of holes with solder paste, pressing heat sink elements down into the holes and heating the solder paste such as to affix the elements in the holes. One drawback with this method resides in the soldering step, a step which the inventive method avoids. The quality of the solder bond is liable to be impaired by subsequent soldering processes carried out in its proximity, particularly when a component is soldered to the heat sink element.
The present invention addresses the problem of enabling components to be mounted more densely on a circuit board than was earlier possible without the heat losses of said components causing the circuit board or its peripheral components to be heated to any great extent.
Accordingly, an object of the present invention is to provide a circuit board manufacturing method which has a heat sink facility that enables components to be placed more densely than is safely possible on other printed circuit boards.
Another object of the present invention is to provide an arrangement which provides a heat sink facility that enables components to be placed more densely than on other printed circuit boards.
In brief, the present invention relates to a method and to an arrangement for providing a printed circuit board that has an appearance which enables a heat sink element to be provided for carrying heat away from a component, said element being firmly held by the circuit board and having effective heat conducting contact with the component concerned. The heat sink element may be in contact with an external cooling surface.
The inventive method has the characteristic features set forth in the accompanying claim 1.
Advantageous embodiments of the inventive method will be apparent from the accompanying claims 2-9.
Characteristic features of the inventive arrangement are set forth in the accompanying claim 10.
Advantageous embodiments of the inventive arrangement will be apparent from the accompanying claims 11-12.
Rapid local heat conduction is achieved with heat sink elements, therewith enabling components to be mounted on the surface of a printed circuit board without needing to pay particular respect to the heat losses of said components. As a result, effective earth contact is also obtained between the underside of the components and the earth plane. In one embodiment of the inventive method, the earth plane in the inner layer of the laminate is also connected electrically to the metal stud. This can be achieved at low cost, without needing to introduce new processes in circuit board manufacture.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.